Analysis of lidar measurements of ice clouds at multiple incidence angles

The focus of this paper is the retrieval of the oscillation angle of crystals around the horizontal plane, in low‐level ice clouds, using the lidar depolarization ratio. An ice cloud located between 0.5 and 2.25 km of altitude has been studied. Measurements were taken near Montreal, on February 2nd, 2000, with a 1.06‐μm lidar with scanning capability and dual polarization. The scanning observations show high variations of both backscattering coefficient and depolarization ratio, that are usually associated with horizontally‐oriented crystals. A technique has been developed to retrieve the average crystals oscillation angle: the evolution of the measured lidar depolarization ratio with the lidar beam incidence angle on the cloud is compared with simulations of lidar depolarization ratio computed through ray‐tracing. For the fore mentioned case, the average crystal oscillation angle is estimated to be 12° and the relative quantity of oriented ice crystals in the cloud to be 20%.